Recently, a plug-in hybrid vehicle in which a driving motor and a charge device (a battery) externally chargeable are mounted, in addition to an engine which is an internal combustion engine has been discussed as an environmentally friendly automotive vehicle. In this plug-in hybrid vehicle, in order to secure a mode (EV traveling mode) electrically travelable only by means of the driving motor, such a battery that a cell capacity is large as compared with a hybrid vehicle which is not capable of being externally chargeable is mounted. Therefore, for a user whose ordinary vehicular travel distance is short, an EV traveling only by means of the driving motor is mainly carried out so that a frequency of starting the engine becomes reduced. Thus, gasoline within a fuel tank is not consumed for a long interval of time so that gasoline is deteriorated due to oxidization.
Therefore, to aim at a reduction of the deterioration of fuel, a control apparatus for a hybrid vehicle in which an engine start timing modification process which modifies an engine start determination value or vehicle requested power on a basis of an estimated degree of deterioration of fuel is executed has previously been proposed (for example, refer to Patent document 1).
However, in the previously proposed control apparatus for the hybrid vehicle, the engine start timing modification process is executed only by estimating the degree of the deterioration of fuel without information on a progress of the fuel consumption within the fuel tank and the progress of the fuel deterioration taken into consideration.
Because of this, when the degree of deterioration is estimated as a predetermined degree of deterioration, for example, under a situation such that a small quantity of fuel is left within the fuel tank and the fuel consumption is advanced in a short period of time, the vehicle runs out of fuel before remaining fuel within the fuel tank is deteriorated even if the engine driving according to a basic control is continued. In other words, under a situation such that the fuel consumption is advanced in the short period of time, a worsening of a fuel consumption rate is introduced due to excessive executions of the engine start timing modification process.
On the other hand, when the degree of deterioration of fuel is estimated to be equal to the predetermined degree of deterioration, for example, under a situation that a long period of time is required for the consumption of fuel, remaining fuel within the fuel tank is deteriorated at an earlier timing even if the engine start timing modification process is continued. In other words, under a situation in which the long period of time is needed for the fuel consumption, the deterioration of fuel cannot be suppressed due to insufficient execution of the engine start timing modification process.